We analysed 195 single best answer MCQs; 95 used text alone and 100 used illustrated text.  The number of students per examination ranged from 277 to 347, with a total of 60,850 student-question interactions.

• There was no difference in item difficulty between the two groups
  
  • (0.76 vs. 0.80; p = 0.862, Mann-Whitney-U).
• The item discrimination (point biserial correlation), also showed no difference between groups
  
  • (0.305 vs. 0.304; p = 0.948; Independent t-test).

With text-alone MCQs, the decision as to whether to use context-free or context-rich questions depends on the specific item context and information required (3). While the use of appropriate illustrations in learning has been shown to facilitate understanding and increase information retention, particularly for delayed recall (4, 5), information on the effect of illustrations in examinations is more limited but suggests that their influence is dependent on context (1).

• We found no overall bias or effect on either item difficulty or discrimination resulting from the addition of illustrations to Single Best Answer MCQs. 

• We suggest that illustrations may useful additions to textual vignettes; whether they test basic recall or more complex reasoning will depend on exactly how they are employed.

• Both illustrated text and text alone MCQs are valid formats for undergraduate histology examinations and may test a range of cognitive levels depending on context.